The objective of this proposed project is to find geographic and more informative tests to detect abnormality in small airways by means of breath sounds. These tests are Opening Sounds Volume and Flow Dependence Breath Sounds Sequence. The Opening Sounds Volume depends on the concept of airway closure. At low lung volumes airways in the dependent part of the lung are closed and there is no ventilation to that part and no breath sounds. As lung volume increases to a certain level dependent airways start to open up and air can get in, producing breath sounds. If there is disease in small airways, the diameter of these airways will be smaller than normal, hence airways will open at a larger lung volume. By recording breath sounds with microphones and electrical amplifier systems and lung volumes simultaneously, we would be able to find out the volumes at which airways open and produce breath sounds. These volumes would be larger if subjects have small airway disease. Flow Dependence Breath Sounds Sequence depends on the concept of inequality of time constants in small airway disease. Two simultaneous breath sounds recorded from two locations of the same horizontal level were plotted against each other on an oscilloscope. If time constants of these two locations are equal, the ventilation of these locations will be in phase and also the breath sounds. The oscilloscopic plot will be a straight line. If time constants are unequal, the oscilloscopic tracing will form a loop with a phase angle. By quantitating the phase angles and plotting them as a function of flow rate we would have some idea of the degree of inequality of time constants, and therefore the degree of small airway disease. Experiments will be done on both normal nonsmokers and smokers with normal routine pulmonary function tests. There will be 10-20 subjects in each group. Currently available physiologic tests for small airway disease will also be performed on all subjects. The sensitivity and specificity of two proposed new tests will be compared with all physiologic tests of small airway disease.